A surprisingly recent instance of human evolution has been detected among the peoples of East Africa. It is the ability to digest milk in adulthood, conferred by genetic changes that occurred as recently as 3,000 years ago, a team of geneticists has found.

The finding is a striking example of a cultural practice  the raising of dairy cattle  feeding back into the human genome. It also seems to be one of the first instances of convergent human evolution to be documented at the genetic level. Convergent evolution refers to two or more populations acquiring the same trait independently.

Throughout most of human history, the ability to digest lactose, the principal sugar of milk, has been switched off after weaning because there is no further need for the lactase enzyme that breaks the sugar apart. But when cattle were first domesticated 9,000 years ago and people later started to consume their milk as well as their meat, natural selection would have favored anyone with a mutation that kept the lactase gene switched on.

Such a mutation is known to have arisen among an early cattle-raising people, the Funnel Beaker culture, which flourished some 5,000 to 6,000 years ago in north-central Europe. People with a persistently active lactase gene have no problem digesting milk and are said to be lactose tolerant.

We don't know. Could be you are suffering from a case of DNA Methylation where something you ingested turned off the gene(s) that produce proteins and enzymes that allow you to metabolize lactose (before it reaches your large intestine and makes you explode, much to your chagrin and embarrassment as your body parts fly around the room).

Or, you might have the gene(s) that turn off at adulthood.

Or, you might well have a totally different gene that's doing something else while it incidentally creates proteins that react against your regular lactose tolerance gene(s).

There are so many possibilities and so little time.

Best bet is to get aholt of some "lactase" pills, or drink milk without lactose.

Not all differences in what appear to be genetic processes are a evolutionary in nature ~ some of them aren't even changes in genes.

Oh, OK. Let's say this "gene" in Africa is different than the one in the rest of the world where people have a gene that allows them to drink milk as adults.

Let's say it's a recessive, and the other one is dominant.

You could have a population of people able to drink milk no matter what, but if the mother were carrying one of each, and had at least two kids, and one kid inherited the dominant gene, and the other kid inherited the recessive gene (the father having had neither gene), one kid could drink milk and other couldn't.

Right in the same family.

So the mad scientist comes along and discovers this family has three lactose handling genes. One dominant ~ to drink. One recessive - to drink. One "old fashioned", and to drink as a child then shut down.

Which, by the way, makes sense for a friend of mine who has several children. Some of them grew up drinking milk into adulthood. Others did so only as children. He could never drink milk, nor could his wife.

The only answer we could come up with was that he and his wife both had at least one recessive for drinking milk but everything we could find suggested the milk drinking gene was dominant.

From this one case I'm going to hazard a guess that the new gene found in Africa is a recessive.

Looks like the two different genetic strains can still cross-breed too! No species difference has yet appeared.

As you mentioned in your earlier post, there are a LOT of possibilities.

I grew up drinking unpasteurized milk. There is quite a bit of difference in milk just in this last generation. Antibiotic "contamination", for one example. Another would be the breed of milk cow. Dairy farms are much rarer now. When you see one, you'll likely see "Holsteins". {colored like a Dalmatian} Not long ago, you would see Jerseys, Guernseys, Milking Shorthorns, and maybe others. The difference in the milk was very noticeable, even though the lactose couldn't be that much different.

I'm fascinated by some old recorded accounts from the Ozarks of an illness called "milk sick". They believed it was caused by the cow eating some type of plant and contaminating the milk. These old doctors could diagnose this condition from the odor when entering the home.

18
posted on 12/10/2006 4:00:42 PM PST
by labette
(Give love to many and trust to few. Always paddle your own canoe.)

I can't remember the specific details. The source is from a series of history books called "Foxfire". I would buy them and give them to my Dad. {After reading them first}

From my own experience, I can't say that I've ever seen cattle eat jimson weed. Simply handling the stuff leaves a smell that is hard to remove. It wouldn't seem to be very tasty. But who knows what an animal stressed with hunger might eat.

23
posted on 12/10/2006 4:36:06 PM PST
by labette
(Give love to many and trust to few. Always paddle your own canoe.)

But when cattle were first domesticated 9,000 years ago and people later started to consume their milk as well as their meat, natural selection would have favored anyone with a mutation that kept the lactase gene switched on.

Why would 'natural selection' favor someone who could drink milk?

25
posted on 12/10/2006 4:39:34 PM PST
by MEGoody
(Ye shall know the truth, and the truth shall make you free.)

There is a significant amount of genetic variation between different etnic groups of humans. Blonde hair and blue eyes were and are a favorable mutation for northern European populations. Why? The paler complexion is more favorable to the absorption of UV light, needed for Vitamin D production.

However, for populations living in tropical regions, a dark skin is a favorable genetic variation. Why? For protection against much higher levels of UV light.

When the gene for sicle cell anemia is heterozygous, the gene offers some protection against malaria. However, when the individual is homozygous for the trait, the person develops sicle cell anemia, a potentially fatal disease.

In general, populations from Northern Europe, cary the gene variation for digesting lactose. The European populations had a greater need for milk, to supply the needed nutrients for producting vitamin D. However, populations from tropical regions had less need for the ability to consume milk, because they receive a lot more sunlight.

Did a quick search, and it wasn't Jimsonweed, it was White Snakeroot. Abraham Lincoln's mother died from milk tainted with it. Sounds like laws were passed about fencing cattle in as a result, since they got into it running free range, it grew in forested areas.

This is not "natural selection" in the sense of which tigers or wolves ate which people, but rather how long the females stayed in good health to breed more babies than the others who couldn't drink cow's milk.

Although we've come up with the term "cheese eating surrender monkey", it's actually the case that those who can eat fresh cheese will probably outlive those who can't.

You have been pinged because of your interest regarding news, debate and editorials pertaining to the Creation vs. Evolution debate - from the young-earth creationist perspective. To to get on or off this list (currently the premier list for creation/evolution news!), freep-mail me: Add me / Remove me

Still human beings, with a mutation acting on what's already there. This isn't anything that helps out neodarwinian evolution at all.

natural selection would have favored anyone with a mutation that kept the lactose gene switched on. Natural selection (better known as ramdom variation)would not favor anyone it selects, and how would it know to select milk drinkers. Natural selection is a random act that brings everything back to the average.

Such a mutation is known to have arisen among an early cattle-raising people, All right which one of them was there because they have the key to long life. Known to have is a definitive statement that can not be made there is know way scientifically to prove that a mutation happened and when.

But the 3000 year thing is close to Biblical flood time of around 4500 years when God told man to eat meat.

48
posted on 12/10/2006 8:49:20 PM PST
by Creationist
( Evolution created it all from nothing in 15 billion years. Thats' not religious faith?)

OK, just one question: Why did our ancestors bother to domesticate milk cows, when they couldn't digest the milk in the first place? Did they know that some day, they would become lactose tolerant? If this is evolution, wouldn't that mean our ancestors had to be drinking milk, as adults, for a long time, in the hope that some day their children, or grandchildren, etc, would mutate that gene? Wow, our ancestors were VERY forward thinking.

50
posted on 12/10/2006 10:09:25 PM PST
by jim35
("...when the lion and the lamb lie down together, ...we'd better damn sure be the lion")

Disclaimer:
Opinions posted on Free Republic are those of the individual
posters and do not necessarily represent the opinion of Free Republic or its
management. All materials posted herein are protected by copyright law and the
exemption for fair use of copyrighted works.